Paid Links Violate Google's Guidelines

Just last week, Google hit a French link network that was in violation of their guidelines and then stated that a Germany network would be the next one that was hit. for those that were hit in the French link network, a notification should have been received from Google as well as a ranking reduction most likely. Earlier in the week, Matt Cutts, head of search spam, posted on twitter that another German violation of paid links has been spotted and basically warned them about it. His exact tweet was:

A reminder(in German) that paid links that pass PageRank violate our guidelines.

It was also posted in a blog post that states unnatural links might receive penalties and that goggle reserves the right to do that. All types of unnatural links are explained in this article. If your site was by chance hit, then it also describes how you can file a reconsideration request.